1. Field of the Invention
The present invention relates to a technique of scanning a frequency band that is cut off when an electromagnetic wave corresponding to the natural frequency of plasma is applied to the plasma in order to use a correlation between the density and the natural frequency of plasma, to measure and monitor the plasma density. Specifically, the present invention relates to a device for measuring and monitoring electron density of plasma, that includes a frequency probe having an antenna structure for scanning plasma while applying electromagnetic waves to the plasma and an analyzer for analyzing a frequency band that is cut off when an electromagnetic wave corresponding to the natural frequency of the plasma is applied to the plasma.
2. Background of the Related Art
Plasma is widely used for manufacturing semiconductor devices because it is required that the semiconductor devices be miniaturized and semiconductor processes be performed at low temperature required. Equipment used for manufacturing semiconductor devices includes an ion implantation apparatus used for implanting desired impurity into a predetermined region of a wafer, a furnace used for growing a thermal oxide film layer, a deposition apparatus used for depositing a conductive layer or an insulating layer on a wafer, and exposure and etching apparatuses used for patterning the deposited conductive layer or insulating layer into a desired shape.
Plasma equipment, which forms plasma in a vacuumed airtight chamber and injects reaction gases into the chamber to deposit a material layer or etch a deposited layer, is widely used as an apparatus for depositing a predetermined layer on a wafer or etching a predetermined layer formed on the wafer. The reason for this is that a material layer can be deposited using plasma at low temperature such that impurities in impurity regions formed in the wafer are not diffused and uniform thickness of the material layer can be obtained even when the material layer is formed on a large-size wafer.
Furthermore, when a predetermined film formed on the wafer is etched using plasma, uniform etch rate over the entire wafer can be obtained.
Langmuir probe is widely used as a device for measuring electron density and ion density of plasma of the plasma equipment. The principle of the Langmuir probe is follows: A probe is inserted into a plasma chamber filled with plasma and varies a DC voltage applied to the probe within a range of −200V to 200V to measure characteristic of the plasma. Here, positive ions in the plasma are collected in the probe when a negative voltage is applied to the end of the probe to generate current based on the ions. When a positive voltage is applied to the end of the probe, electrons in the plasma are collected in the probe to generate current based on the electrons. Then, the plasma density is obtained by measuring the generated current and analyzing a correlation between the current and the voltage applied to the probe.
The conventional Langmuir probe can measure plasma density in real time because it inserts the probe into the chamber to measure the plasma density. However, the conventional Langmuir probe is difficult to use for the actual mass production because noises are generated due to RF oscillation, a thin film material is deposited on the probe when a process of depositing the thin film material is performed to fabricate a semiconductor device, and the probe is etched when dry etch is carried out.
In the meantime, a plasma oscillation probe and a plasma absorption probe have been developed as a tool for monitoring a plasma process. However, these devices cannot be appropriately utilized for the actual mass production.
A conventional plasma oscillation probe uses a hot wire to generate an electron beam. The hot wire is cut at high pressure of higher than 50 mT and thus operating conditions of the plasma oscillation probe are narrowly restricted. Furthermore, when the hot wire is heated in order to emit hot electrons, the hot wire is evaporated to contaminate a reaction chamber.
For a conventional plasma absorption probe, there occurs a problem in that it should be calibrated using an accurate plasma density test tool before being operated. Although there has been proposed an improved probe structure, it requires a number of calculation steps for calculating the absolute value of a measured density. Here, physically assumed conditions are included in the calculation steps so that effectiveness of the measurement of the plasma density is decreased.